1. Field of the Invention
Brake systems including vacuum operated brake boosters.
2. Prior Art
Vacuum operated brake boosters in brake systems are conventionally operated at differential pressures ranging between 0.7 and 0.8 bars. In an Otto cycle engine powered automotive vehicle it has been conventional practice to utilize the vacuum in the induction pipe of the carburetor (or intake manifold) as the vacuum source for such brake boosters. In recent years because of the legal regulations in respect to exhaust emission control many of the automotive vehicles having Otto engines no longer generate a desired vacuum of a 0.2 to 0.3 bars. In order to achieve a sufficient brake boosting effect utilizing a vacuum operated brake booster, the diameters of such brake boosters had to be enlarged in order to achieve the same braking force with the smaller pressure differential available. Other efforts which have been made to make use of the small pressure differential reside in providing brake boosters with two pistons arranged in tandem. In some cases it has been advantageous to utilize a separate vacuum pump as the vacuum source instead of using the carburetor induction pipe or intake manifold. This latter solution has become common practice in diesel-engine cars. In each of the above instances the various methods employed render a brake system considerably more expensive. Furthermore to make the brake booster larger in diameter is often not possible because, for engineering reasons, the space available under the hood for mounting the brake booster has become more and more restricted due to the increasing tendency towards compact cars.